Since melanin synthesis is a specific differentiated function of melanocytes and tyrosinase is a specific enzyme in melanogenesis, tyrosinase should be a good marker for melanoma, which is a malignancy of melanocyte. On this basis we wish to achieve the following objectives: 1. To develop a simple procedure to purify tyrosinase from human malignant melanoma tissue. 2. To develop a radioimmunoassay for measuring tyrosinase levels in physiological fluids from patients with malignant melanoma. 3. To perform comparison study of tyrosinase activity assay and the radioimmunoassay method. 4. To ascertain the value of the radioimmunoassay in diagnosis, examining efficacy of various treatments and follow-up studies of patients with malignant melanoma in the early detection of malignant melanoma. 5. To localize tyrosinase in established cell lines of human malignant melanoma with the aid of the antibody produced against the tyrosinase.